The Gray Ghost, played by actor Simon Trent, was a fictional television hero from Bruce Wayne's childhood. Before his parents' death, Bruce often watched The Gray Ghost on television with his father. The dynamic costumed vigilante helped shape the vigilante persona Bruce Wayne adopted later in his life, the cape and cowl of the Dark Knight.

Decades later, however, Simon Trent was little more than a washed up, typecasted actor. Unable to pay his rent, he slowly sold his Gray Ghost memorabilia to cover the bills. Frustrated with his life, he regretted his decision to ever play The Gray Ghost, destroying the few pieces of the collection he had left. However, fate, chance or perhaps just very careful planning brought Batman into contact with Trent. Though he was investigating a bombing spree similar to one depicted in The Gray Ghost, Batman revealed to Trent the importance and influence the character had on him in his early years.

Trent realized the worthiness of his role as the Gray Ghost after seeing the Batman's personal collection of Gray Ghost merchandise and he was glad that what he had done had a positive influence. Trent redeemed himself, donning The Gray Ghost persona once more, and aided Batman in unraveling the mystery of The Mad Bomber. The Bomber turned out to be a toy collector who used Trent's memorabilia to re-enact an episode of The Gray Ghost.

Shortly thereafter, a major home video release of the long lost TV series was made from Trent's personal film collection, likely making him a wealthy man. During a public video signing (in costume), Bruce Wayne acquired Trent's autograph and subtly revealed to his hero his own secret identity, which pleased Trent to no end. It is assumed Trent kept the secret to himself.

The Gray Ghost is voiced by Adam West, the actor who played Batman in the 1960s TV series and associated movie. Bruce Timm and Paul Dini have stated that they would not have made the episode in which he appears if West had turned down the part, as they feared he would be offended by an animated parody of the typecasting he reportedly suffered in his later career. West, however, was happy to voice the character.

Several Gray Ghost posters make appearances in the backgrounds of various episodes.

Over time, Bruce Wayne filled the Batcave with multiple pieces of memorabilia from his life. One piece is a The Gray Ghost outfit. It's unknown if it is the original or a replica Bruce obtained.

In the 2015 game Batman: Arkham Knight, in Oracle's clock tower there is a poster for "The Ghost in Gray", a tribute to The Gray Ghost from BTAS.